A client device as defined in the present disclosure is a device that may access voice, video, text, instant messaging, internet and other services from a wireless communication network. Such client devices may include conventional devices such as a smartphone, a tablet, a feature-phone, a laptop or a desktop personal computer, etc. Other client devices may include devices that are embedded within devices that perform other functions such as an entertainment system in a home or in an automobile, a home appliance such as a refrigerator or washer/dryer, a wristwatch with a heart rate monitor, a medical device such as a blood pressure meter or insulin sensor, a utility meter, a gaming console, a camera, a navigation device, an industrial equipment, etc.
The wireless communication networks are often referred to as Wireless Wide Area Network (WWAN). The internet service offered by such networks is often referred to as mobile broadband internet or Mobile Broadband (MB) and the WWANs are often referred to as mobile broadband networks. The terms WWAN and MB are used interchangeably herein. An example of a mobile broadband network is the Long Term Evolution (LTE) from the 3rd Generation Partnership Project (3GPP). The LTE technology and its evolution are often referred to as fourth generation (4G) technologies. A client device may also use any of the previous generation technologies such as “2G”, “3G” from 3GPP and other standardization bodies. A client device may also use future generation technologies for mobile networks. Typically, as shown in FIG. 1, a WWAN comprises elements such as client devices or mobile stations and one or more base stations. Other network devices may also be employed, such as a mobile switching center (not shown). As illustrated in FIG. 1, the communication path from the base station (BS) to the client device or mobile station (MS) is referred to herein as a downlink (DL) direction or downlink channel. The communication path from the client device to the base station is referred to herein as an uplink (UL) direction or uplink channel. In some wireless communication systems, the MS communicates with the BS in both the DL and UL directions. For instance, such communication is carried out in cellular communication systems. In other wireless communication systems, the client device communicates with the base stations in only one direction, usually the DL. Such DL communication may occur in applications such as paging. Typically in a wireless communication system, the client device and the base station may transmit information in blocks of data and such a block of data is referred to herein as a “message.”
A base station to which a client device may be downlink synchronized and/or communicating with at any given time is referred to herein as the Serving Base Station (SBS). In some wireless communication systems the serving base station may be referred to as the serving cell. The base stations that are in the vicinity of the serving base station are called Neighbor Base Stations (NBS). Similarly, in some wireless communication systems a neighbor base station may be referred to as a neighbor cell.
A client device, after initially synchronizing with a cell, may switch to another cell depending on the signal conditions, network congestion, and other criteria. The process of switching from one cell to another cell by a client device is often referred to as handover (HO) or cell reselection. In some wireless communication systems handover is also referred to as handoff. Also in some wireless communication systems cell reselection is also referred to as idle mode handoff. An NBS, to which a client device may be switching over its communication from the current SBS, is herein referred to as Target Base Station (TBS). In some wireless communication systems, a target base station is normally referred to as a target cell. Sometimes, during a handover, the serving cell and the target cell may be the same and only the channel used for communication may be changed. Such a handover, in which the cell is not changed, is called as an intra-cell handover. The purpose of intra-cell handover may be that the new channel is better suited for communication than the previous channel within the same cell. Cell reselections or handovers amongst cells that use the same frequency are referred to herein as intra-frequency cell reselection or handover. Cell reselections or handovers amongst cells that use different frequencies are referred to herein as intra-frequency cell reselection or handover. A network may use different Radio Access Technologies (RATs) for providing various services. In a particular network, the cells of different RAT types may be overlapping or adjacent to each other. If a neighbor cell is using a RAT type that is different from the RAT type used by the serving cell, it is referred to as an inter-RAT neighbor cell.
The decision making process for handovers and cell reselections varies from one wireless communication system to another. However, the decisions are generally based on the signal conditions measurements by the client devices and reporting of those measurements to the wireless communication network by the client devices. The wireless communication network generally may influence and control the measurements and reporting process of the client device by providing parameters for the measurement and reporting process. The actual decision to perform handover may be made either by the wireless communication network or by the client device depending on the type of particular wireless communication system. On the other hand the cell reselection decisions in idle mode (i.e., when client device is not in active communication with the wireless communication network) may be generally performed autonomously by the client device. Both handovers and cell reselections may normally lead to change of cell from which the client device may access communication services. The difference between the handover procedure and cell reselection procedure depends generally on whether a client device is engaged in an active communication with the wireless communication network.
Normally, certain types of system information may be required by all client devices so that they may communicate with the wireless communication network. The system information typically includes system synchronization information, system parameters, resource allocation information, paging information, etc. The wireless communication network may transmit such system information as broadcast data so that all client devices within its coverage area may be able to receive that information. Such information is herein referred to as “broadcast messages.”
Typically in a wireless communication system a base station may group the system information and each group of system information may be transmitted as multiple broadcast messages and such broadcast messages are herein referred to as system parameter messages. The system parameter messages may carry important system information without which the client device may not be able to communicate with the wireless communication network. The wireless communication network may transmit these system parameter messages at regular intervals in such a way that any client device that enters its coverage area may receive these system parameter messages and may be able to communicate with the wireless communication network at the earliest possible time. Client devices that are already in the base station's coverage area may also periodically receive these system parameter messages for possible updates. Normally a client device may store the system parameter messages in its memory for the current SBS.
Typically, in wireless communication systems, most of the system parameter messages may not change frequently. For example, some system parameter messages may change once or twice a day and some system parameter messages may not change for many days.
In some wireless communication systems, when a client device switches to a new base station due to cell reselection or handover, it may be required to receive the system parameter messages for the new SBS and certain system parameter messages for the selective list of NBSs corresponding to the new SBS.
The set of all system parameter messages broadcast by a base station is herein referred to as “base station broadcast system information.” The individual block of system information message may be referred to as System Information Block (SIB). Two or more SIBs may be grouped and sent as a single System Information (SI) message. There may be different SIBs describing different groups of system parameters such as SIB Type1 (SIB1), SIB Type2 (SIB2), etc. The SI for one or more cells may be periodically updated by the network. To ensure that the client devices are using the correct version of the SI, a field referred to herein as “change-mark” is generally included in the SI messages. A client device may store the change-mark of the SIs it has decoded. If the new SI is transmitted by a cell, it may increment the change-mark to enable the client terminal to detect that it needs to acquire the newly updated SI. The change-mark of the newly acquired SI is then used as latest version for detecting any future changes in the SI. The change-mark field may be incremented in modulo arithmetic to keep the field bit-width to a minimum. For example, the change-mark may be incremented modulo-8 and the value may be represented by a 3-bit wide field.
In idle mode, a client device for the most part may turn off a majority of its circuitry to reduce power consumption. This is often referred to as “sleep” state, a sub-state within the idle mode. A client device may remain in a sleep state for a long duration and may wake up at the desired time window where it expects to receive the paging messages and certain SIBs. This alternating sequence of sleep and wake-up in idle mode is referred to herein as Discontinuous Reception (DRX). The sleep and wake-up sequence may follow regular pattern and its period is often referred to as DRX cycle. The success rate for the incoming calls (e.g., mobile terminated voice calls and/or data calls) in a client device is directly related to the successful reception of paging messages. Normally, in idle mode, in addition to the reception of paging messages and SIB messages, a client device may continue to search and monitor neighbor cells.
When a client device performs a network registration procedure to get service from a cell, it decodes the system information broadcast in the cell. The client device may store such system information. The system information carries important information regarding the cell reselection criteria. Such information includes but not limited to the tracking area identity (TAI), Public Land Mobile Network Identity (PLMN ID) which uniquely identifies a particular network operator, Closed Subscriber Group Identity (CSG ID), RAT types, neighbor cell frequencies, etc. This information may help to decide whether a cell is a “suitable cell” for the client device to avail all the services offered by it, or the cell is an “acceptable cell” where the client device may avail only limited services such as emergency calls. The client device may have to perform the network registration procedure to get service from the network and for the network to be able to page the client device for mobile terminated (incoming) calls. The network registration procedure may be typically performed by a client device with a particular cell. A group of cells in the geographic vicinity of each other may form a registration area. A registration area may be identified based on the system information of a cell. For example, the TACs of a group of cells in a registration area may be the same.
Each base station in a wireless communication network may be identified by a unique identifier referred to herein as Cell Identity (CID). The CID of a base station may become known to a client device when it decodes SI from the base station. To avoid unnecessary updates from a client device and yet ensure the ability to reach a client device at any given time, the network may organize a group of cells into a “tracking area” and use a Tracking Area Identity (TAI) to identify the various groups of cells. This is shown in FIG. 2 where four different tracking areas are illustrated. A cell may broadcast information about the tracking area it belongs to by including the TAI information in the system information. A client device may be required to inform the network when it begins to receive service from a cell that belongs to a tracking area that is different from the tracking area of the cells from which it was previously receiving service. The process of informing the network that the client device has begun receiving service from a cell that belongs to a new tracking area is referred to herein as Tracking Area Update (TAU) procedure. With this method, a client device performs TAU only when there is a change in TAI of the cell from which it is getting service. For example, in FIG. 2, when a client device reselects from the cell with CID=1003 to the cell with CID=1007 which has the same TAI, it may not perform TAU procedure. However, when the client device reselects from the cell with CID=1007 and TAI=200 to the cell with CID=1012 and TAI=201, it may perform TAU procedure.
Different client devices may be identified using their respective unique identities. For example, International Mobile Subscriber Identity (IMSI), Temporary Mobile Subscriber Identity (TMSI), the Media Access Control (MAC) address, the Internet Protocol (IP) address may be used for the identity. Regardless of any particular identity used, it is generically referred to herein as Client Device Identity (CDI).
As long as a client device is in the same registration area, the client device may not perform network registration procedure again except that a periodic network registration update procedure may need to be performed even if the client device continues to move within the same registration area. If the client device moves to a cell which does not belong to the registration area in which the client device is registered, then the client device may perform network registration procedure to get access to and service from the network.
When a client device is in idle mode, the network may only be aware of the location of the client device at the registration area level. In order for a network to page a client device, it may need to send the paging message in all cells belonging to the same registration area. The instances for paging message transmission, known as paging occasions (POs), are usually derived based on a client device's unique identity and the paging cycle. The network may transmit a paging message addressed to a specific client device in its specific PO. When a client device performs cell reselection, the exact instances of paging occasions may be different in the new serving cell. Depending on the exact timing of the cell reselection and the timing of the POs in the old serving cell and the new serving cell, the client device may potentially miss a paging message or may receive it with delay. A single paging message received in a single PO may include multiple paging records to page multiple client devices. Different client devices may be identified within a paging message by using their respective unique identities in the paging records. For example, International Mobile Subscriber Identity (IMSI) may be used for the identity, or in case of 3GPP LTE wireless communication system, System Architecture Evolution (SAE)-Temporary Mobile Subscriber Identity (S-TMSI) may be used.
As the variety and number of client devices have increased, often there may be multiple client devices in close proximity of each other. For example, a number of smartphones, tablets, entertainment systems, gaming consoles, navigation systems, etc. with connectivity to the wireless communication network may be present in a home, an office, a car, etc. There may be a need for the client devices to communicate with other client devices that may be in their close proximity. Therefore, in addition to the connectivity to the wireless communication network, the client devices may have other short range wireless connectivity interfaces to directly connect with each other without relying on a WWAN. Examples of such Short Range Wireless Links (SRWL) may include Wireless Local Area Network (WLAN) commonly known as Wi-Fi, Bluetooth™, or some other local area wireless networking schemes. The SRWLs may operate in a one-to-one or one-to-many mode of communication. For example, the WLAN may operate in an infrastructure mode in which the client devices communicate through an Access Point (AP) that may serve as a bridge to other client devices and other network elements such as internet. The WLAN may also operate in an ad hoc mode in which the two client devices may communicate directly with each other in a peer-to-peer manner. In general the SRWL may use any one of the well known networking topologies such as point-to-point, bus, star, ring or circular, mesh, tree, hybrid, or daisy chain. An example of this scenario is illustrated in FIG. 3 which includes the WWAN 302 and the SRWL 304 between the client devices Smartphone 308 and Smartphone 310. The SRWL 304 has the coverage area 306. The two client devices Smartphone 308 and Smartphone 310 are connected to the WWAN and directly with each other over the SRWL. The client device Smartphone 312 is connected to the WWAN but it is outside the coverage area of the SRWL.
Two or more client devices in a given area may be camped on the same or neighboring cell of the same WWAN, and both the client devices may be performing serving and neighbor cell measurements. This may be an inefficient method of measurements since most of the client devices which are connected on the same SRWL may be camped on the same or neighboring cell of the same WWAN.